1. Field of the Invention
The present invention relates to an image processing circuit and a method thereof. More particularly, the present invention relates to an image processing circuit and a method thereof for enhancing text displaying.
2. Description of Related Art
With growing popularity of the Internet, some network service providers cooperate with publishers or libraries to digitalize books originally published in printings. Then, image data of the digitalized books are provided to Internet users for downloading in a paid or a free approach. Moreover, with fast growing of global population, and considering limited utilization spaces, to effectively utilize spaces, some enterprises or families also try to digitalize printed data via digital cameras or scanners. However, massively digitalisation of texts results in a fact that some texts recorded by digital images are blurry and hard to be read, and therefore it is inconvenient for the users to read such images shown on a display.
Conventional enhancement of read comfort for a digital display is to adjust a color temperature thereof, though there is no special processing method for the texts. Such processing method has no actual improvement for documents with low contrast, especially for scanned documents. Since text information in an image belongs to a high-frequency signal, if the text information is to be enhanced, a sharpening process is generally applied. Though such processing method is the most directive, it still cannot improve the read comfort.
FIG. 1 is a diagram illustrating a relation between luminance values of a plurality of pixels P1 to P18 of a display, and corresponding luminance regulation values thereof. In FIG. 1, the pixels P1 to P18 are arranged in a row, and the horizontal axis represents relative positions of the pixels P1 to P18 on the display. The left vertical axis represents the luminance values of the pixels, and the right vertical axis represents the luminance regulation values of the pixels. To avoid confusion, the luminance value of each pixel is represented by a bold solid line 10, and the corresponding luminance regulation value of each pixel is represented by a non-bold solid line 12. In the present embodiment, the luminance value of each pixel is within a range of 0 to 255, and the brighter the pixel is, the greater the luminance value thereof is; conversely, the darker the pixel is, the smaller the luminance value thereof is. The luminance regulation values of the pixels may be positive, negative or zero, and if the luminance regulation value is positive, it represents the luminance value of the corresponding pixel is enhanced, so that the pixel becomes brighter; if the luminance regulation value is negative, it represents the luminance value of the corresponding pixel is decreased such that the pixel becomes darker; and if the luminance regulation value is zero, it represents that no adjustment is performed to the luminance value of the pixel. For simplicity's sake, the luminance value and the luminance regulation value of the pixel are represented by the same unit in FIG. 1, and a coordinate of the luminance regulation value 0 on the right vertical axis is corresponding to a coordinate of the luminance value 127 on the left vertical axis. Each of the pixels is grouped into a bright portion or a dark portion according to the luminance values thereof, wherein all of the luminance values of the pixels in a bright portion are greater than or equal to 127, and all of the luminance values of the pixels in a dark portion are less than 127. For example, the pixels P1 to P5 and the pixels P13 to P18 are respectively in two different bright portions, and the pixels P6 to P12 are in the dark portion between the two bright portions.
In case that a background portion of an image is brighter than a text portion of the image (for example, an image with white background and black texts), the bright portion corresponds to the background portion of the image, and the dark portion corresponds to the text portion of the image. Due to a characteristic of texts, a simplex sharpness filter may impose a high pass enhancement respectively to the bright portion and the dark portion. As shown in FIG. 1, luminance values of the pixels P5 and P13 in the bright portion and located adjacent to the dark portion may be enhanced (i.e. the luminance regulation values thereof are positive), and luminance values of the pixels P6 and P12 in the dark portion and located adjacent to the bright portion may be decreased (i.e. the luminance regulation values thereof are negative). However, in case of the white background and black texts, enhancement of the bright portion leads to an adverse effect of ringing to the text portion, so that the texts may be looked more uncomfortable. Moreover, if settings of the luminance regulation values are not suitable, an over-shoot or an under-shoot phenomenon may be occurred. In addition, noise interference of an analog-to-digital converter (ADC) also causes an abnormity of the image, and accordingly the user may have an uncomfortable feeling when observing the image.
Moreover, a conventional method for enhancing text displaying is to perform separate treatment to the text portion or non-text portion (such as figures or pictures, etc.) based on a setting of a threshold value. However, in a system with relatively great noise at an input terminal thereof, such method may leads to a situation that identical graphic information displays differently in different frame periods due to an interference of the noise. Therefore, the display quality is lower.